This research project is aimed at an elucidation of the biochemical structure of membrane sites that are involved in the control of ion permeability in nerve and muscle. Reactive groups of membrane proteins and lipids will be chemically modified by reagents of known specificities. Resultant effects on excitation will be quantitated by a $ series of electrophysiological and pharmacological techniques. In this way, residues associated with individual aspects of excitation will be identified, and their role characterized. Most functional aspects of excitation are no longer measurable after membrane disruption, and it is therefore helpful to label components of interest with covalently bound ligands that will be detectable by physical or chemical means after solubilization. The reagents used for chemical modification are therefore potentially useful as labels if they contain a radioisotope, or sufficient color or fluorescence. Several methods are proposed for increasing the specificity of labeling to components of interest which will then be analyzed biochemically with a number of methods with a high degree of resolution. Another aspect of this general problem involves a determination of the density of receptors for tetrodotoxin, a potent and specific inhibitor of sodium channels, in surface and transverse tubule membranes of skeletal muscle cells. These experiments will also provide a value for the conductance of a single open sodium channel. Our goal in this work is to obtain information that may lead to a better understanding of the mechanism of action of neuropharmacological agents and ultimately allow the rational design of drugs, including anesthetics, with high specificity.